1. Field of the Invention
The present invention relates to an automatic running vehicle of the electro-magnetic induction type in which the vehicle is made to run automatically along an electro-magnetic induction line installed in a running track. In more particular, the invention concerns with the automatic running vehicle of the type in which a bogie is provided with detection coils each at the center, left- and the right-hand locations thereof to detect the magnetic field generated by the electro-magnetic induction line installed along the running path and the vehicle is caused to run automatically along the electro-magnetic induction line in dependence on the voltages induced in the center and the right-hand detection coils or alternatively in the center detection coil and the left-hand detection coil with each other. The automatic running vehicle of such type is disclosed in U.S. patent application Ser. No. 539,424, now U.S. Pat. No. 4,006,790.
2. Description of the Prior Art
In the vehicle system of the above described type, it is known that, even if amounts of deviations of the vehicle body to the right or the left side from the center position are equal to each other when the vehicle is running in dependence on the steering voltage derived from the voltages induced in the center detection coil and the selected one of the voltage induced in the right-hand detection coil and the left-hand coil, the steering angle (angle in the absolute value in the sense that no direction is taken into consideration) will take different value in both cases.
In the first place, description will be made on a typical example of the hitherto known automatic running vehicle by referring to FIGS. 1 to 5. In FIG. 1A, reference numeral 1 denotes a bogie provided with a right-hand detection coil 2, a center detection coil 3 and a left-hand detection coil 4. An electro-magnetic induction line 5 is installed in the running ground 6. An alternating current flows constantly through the induction line 5. Magnetic flux produced by the current will be distributed in a pattern of coaxial circles around the line 5, in which the magnetic flux just above the induction line 5 extends in the horizontal direction. Accordingly, the output from the individual detection coils will become zero when the coils are positioned directly above the induction line 5. As the detection coils are displaced away from the position above the induction line 5, the absolute value of the respective output voltages thereof will increase, in which case the polarity thereof is decided in dependence on the direction of the flux. When the amount of the displacement of the detection coil exceeds a predetermined value, the output therefrom will then begin to decrease. Such characteristic of the output voltage of a detection coil is graphically represented in FIG. 2 by a curve 7. In this figure, then induced output voltage is taken along the ordinate, while the distance between the detection coil and the induction line is taken along the abscissa. The negative value of the induced voltage means that the direction of the influential magnetic flux is opposite to that of the magnetic flux inducing the positive voltage. When the alternative current is used, it is preferred that a dual wire parallel line such as a feeder line for a television receiver, for example, should be employed in an arrangement schematically shown in FIG. 1B.
The steering signal can be derived by composing the vector of the output from the center detection coil 3 and that of the right-hand detection coil 2 or that of the left-hand detection coil 4. In FIG. 3, the output signals from the center detection coil 3 and the left-hand detection coil 4 which are assumed to be used for producing the steering signal by way of example are illustrated simulatively by straight line segments. It will be appreciated that the same signal waveforms may be obtained with the polarities thereof being inverted when the center detection coil 3 is used in combination with the right-hand detection coil 2. In FIG. 3, reference character L represents the distances between the center detection coil CC corresponding to the coil 3 in FIG. 1A and the left-hand detection coil LC or coil 2 in FIG. 1A and between the former and the right-hand detect coil RC or coil 4 in FIG. 1A. The distance between the coils CC and LC is equal to the one between the coils CC and RC and remains constant since these coils are fixedly secured to the bogie 1. Curve 8 represents the characteristic of the voltage induced in the center coil CC, while curve 9 represents the voltage characteristic of the output signal from the left-hand detection coil LC. It is to be noted that, although the curve 9 follows in reality the profile of curve 8, the former is shown as shifted to the right by the distance L for the convenience' sake of illustration to show the addition of both signals. The steering signal is derived by composing vectors of the induced voltages represented by the curves 8 and 9. The steering signal thus obtained is shown by curve 10 in FIG. 3. In this way, mere composition of the outputs from the left-hand detection coil LC and the center detection coil CC results in the steering signal of the waveform shown by the curve 10 which however has zero point 0' shifted to the right-hand side by .DELTA.L from the actual zero point 0, as viewed from the plane of FIG. 3. Usually, the vehicle is steered on the basis of the imaginary zero point 0' utilized as a reference for the steering. On the other hand, in the case where the right-hand detection coil RC is employed in combination with the center detection coil CC, the corresponding zero point is shifted to the left by .DELTA.L to -0'.
FIG. 4 illustrates a rightwardly shifted running path 11 of the vehicle steered in accordance with the steering signal derived from the output signals of the center and the right-hand detection coils CC and RC as well as a leftwardly shifted running path 12 of the vehicle when the center and the left-hand detection coils CC and LC are employed. Since the running path of the vehicle will become different considerably in dependence upon whether the right- or left-hnd detection coil RC or LC is used together with the center detection coil CC as can be seen from FIG. 4, there may arise difficulties such that different distances between the vehicle and an unloading platform 13 may provide an obstacle in the transporting works of the loads from the vehicle 1 to the platform 13, for example. In particular, when the unloading operation is to be carried out automatically, variations in the distance between the vehicle 1 and the platform 13 makes the load transferring operations remarkably difficult. Furthermore, when the vehicle is changed over from the right side running path 11 to the left side running path 12 during the running of the vehicle, there may arises a danger of meandering movement of the vehicle 1 such as shown in FIG. 5. Such danger will of course increase particularly when the running vehicle is transporting a great amount of load or running at a high speed. Even in the case where the deviation of the running path can be tolerated, it is inevitable that unnecessary large width of the running track is required. Besides, the danger that the vehicle should strike against men working in the track area has to be considered.